Methods and apparatus for handheld printing with optical positioning

ABSTRACT

Methods and apparatus include a handheld printer manipulated by an operator to print an image on a media. A controller correlates a location of a printhead to the image and causes printing or not. A position sensor provides input to the controller. Its signal typifies pixels in a matrix frame indicating a current position frame and, over time, a previous position frame. The controller compares the two frames to find a presence of the previous in the current. To improve computational efficiency, the controller reduces a relative size of both frames before comparing. Specific reduction techniques contemplate converting a matrix frame of pixels indicative of previous and current locations into smaller matrices, including one-dimensional forms. Possible search areas within the current frame to look for the previous frame utilize knowledge about the movement history of the printer. Position sensor signal validity and controller architectures are other noteworthy features.

This application claims priority to and benefit of U.S. ProvisionalPatent Application Ser. No. 60/827,117, filed Sep. 27, 2006, entitled“Optical Navigation System using Reduced Reference and Sample Objectsand Enhanced Target Tracking Method.”

FIELD OF THE INVENTION

Generally, the present invention relates to handheld printers.Particularly, it relates to improving print quality in handheld printersof the type able to print in random motion patterns. In one aspect,sensors optically provide position information of the printer regardlessof user movement patterns. In another, particular printer controlarchitectures are contemplated. Still other aspects relate tocomputational efficiencies relative to position sensor signals. Othernoteworthy features relate to assessing validity of position sensorsignals.

BACKGROUND OF THE INVENTION

As is known, handheld printers afford mobile convenience to users.Unlike their immobile or stationary counterparts, users determine thenavigation path of a given swath of printing. In some instances, thisincludes random movement over a media. In others, it includesback-and-forth movement attempting to simulate a stationary printer.Regardless, successful handheld printing dictates that image informationrelative to the printer location be available at all times. However, allusers do not navigate in the same fashion. Nor do they navigate at thesame speed or housing orientation. For at least these reasons, handheldprinters rely heavily on sensor inputs, such as those from opticalsensors or encoders, for printing images. Yet, sensor inputs aresometimes limited in their capabilities and print jobs are interrupteddue to lost or inaccurate printer location calculations.

If the printer location ever becomes lost, the printer can either quitprinting or guess at location. If printing quits, users have incompleteprint jobs. If locations are guessed, print quality suffers. In either,poor results are obtained. In the event printer locations are notcompletely lost, but simply inaccurate, print quality suffers because ofinappropriately placed ink print patterns being deposited on the media.Error accumulation also adds to the problem of ink placement.

To overcome this, certain prior art has suggested sensors that identifytypographic structures on the media to determine position of theprinthead relative to the paper. This has shortcomings, however, forwant of positioning assistance in areas or regions of the media where notypographic structures exist.

In other art, optical sensors are employed to correlate currentlocations to previous locations to find a delta between the locations.Appreciating typical optical sensors have numerous data pixels,correlation becomes computationally extensive because comparisons oflarge amounts of pixel data to other large amounts of pixel data requirelarge storage and processing power. Because the sensors also samplefairly rapidly, the volume of pixel data increases quickly therebyrequiring correlation techniques to have relatively fast processingtimes.

Accordingly, there exists a need in the art for robust,multi-directional and random printing handheld printers having improvedprint quality. Particularly, there are needs by which handheld printersare able to ascertain position regardless of particularized media areaor regions. The need further extends to processing of sensor signalswith less computational complexity while still remaining fast andpowerful. Naturally, any improvements should further contemplate goodengineering practices, such as relative inexpensiveness, stability,flexibility, ease of manufacturing, etc.

SUMMARY OF THE INVENTION

The above-mentioned and other problems become solved by applying theprinciples and teachings associated with the hereinafter describedhandheld printing with optical positioning. Specifically, methods andapparatus contemplate handheld printers manipulated randomly orpredictably over a media on which an image is printed. In this regard, aposition sensor transmits and receives light from the media and anoutput signal thereof is provided to a controller to assist inascertaining positioning of the printer regardless of how users maneuverthe printer. Over time, the position sensor signal typifies a previouslocation and a current location. The controller searches the currentlocation for a presence of the previous location and correlates same toa printhead for printing the image or not. To improve computationalefficiency, the controller reduces a relative size of the signals fromthe position sensor before conducting the searching. In a basic sense,the previous frame of pixel data is reduced in size to a target frame,in turn, reduced to a one-dimensional matrix form. The current frame isreduced in sized to a two-dimensional form with one-dimensional portionsthereof, having a same size as the one-dimensional matrix form of theprevious frame, being searchable for a presence of the one-dimensionalmatrix form. In a correlation matrix, a highest correlation betweenvalues of the one-dimensional matrix form and the one-dimensionalportion of the two-dimensional current frame indicate the presence ofthe previous in the current. In this manner, aspects of the inventiondefine an optical navigation system for a handheld printer that buildsupon prior art correlation approaches between past and presentpositioning signals, or data, for determining movement. It features theuse of variations in computation of correlation and other distortionfunctions to minimize computation. The navigation system also employs anenhanced search algorithm to further reduce significantly thecomputation thereby making it fit for real-time application.

Methods and apparatus further include handheld printers manipulated backand forth by an operator during use to print an image on a media. Theimage is printed with various actuators of an inkjet printhead and acontroller correlates the location of the printhead to the image andcauses printing by the actuators or not as a user maneuvers a housing ofthe printer. A position sensor, preferably optical, provides input tothe controller. The sensor is also representatively an off-the-shelftype sensor to facilitate manufacturing simplicity and minimize costs.Its signal typifies a plurality of pixels (representing grayscale valuesof light reflected from the media) in a matrix frame indicating acurrent position frame and, over time, a previous position frame. Thecontroller compares the two frames to find a presence of the previousposition frame in the current frame, in turn, ascertaining a location ofthe printer and printhead. As before, the controller reduces a relativesize of both frames before the step of comparing to improvecomputational efficiency, especially by way of speeding-up the processof evaluation. Specific reduction techniques contemplate converting amatrix frame of pixels in m×n form indicative of a previous and currentlocation, where m and n may equal one another, into smaller matrices,including one-dimensional and square matrix forms. Possible search areaswithin the current frame showing a presence of the previous frameutilize knowledge about the previous movement history of the printer topredict where-to-look locations.

Position sensor signal validity and handheld printer controllerarchitectures are other noteworthy features. For example, positionsensor signal validity contemplates an intake checker between the sensorand controller, or as part and parcel of the controller, that arrangesthe information of the sensor signal so that a relative distance betweenthe housing and the media can be ascertained. It also contemplatesestablishment of a threshold inquiry determining whether the housing ofthe printer is relatively close or far away from the media and whethersuch is sufficient to conduct further signal processing. Validitychecking also considers application per every signal received from thesensor or application randomly, on occasion or at predetermined timeintervals.

In still other embodiments, architecture of the handheld printercontemplates one or more position sensors, a controller and an inkjetprinthead that are coordinated to print an image. As part of thefunctionality of the controller, such as part of an ASIC, discretechips, a microprocessor, software, firmware, etc., the controllerincludes one or more of: a transformer or reducer to reduce a relativesize of the output of the position sensor, including a summationcomponent to sum full or partial rows or columns of the matrix form ofthe position sensor signal to make the signals smaller; a comparator toascertain differences between position sensor signals indicative ofcurrent and previous locations, or to find a presence of the previouslocation within the current location; and a navigation output calculatorto track and make inferences/calculations contemplating prior movementsor history of the printer housing movement when examining possiblesearch areas within the current location for instances of the previouslocation. Local or remote storage for the controller is alsocontemplated.

These and other embodiments, aspects, advantages, and features of thepresent invention will be set forth in the description which follows,and in part will become apparent to those of ordinary skill in the artby reference to the following description of the invention andreferenced drawings or by practice of the invention. The aspects,advantages, and features of the invention are realized and attained bymeans of the instrumentalities, procedures, and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification, illustrate several aspects of the present invention, andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a diagrammatic view in accordance with the present inventionof a handheld printer;

FIG. 2 is a diagrammatic view in accordance with the present inventionof a representative inkjet printhead for use in the handheld printer ofFIG. 1;

FIG. 3 is a diagrammatic view in accordance with the present inventionof a representative control arrangement of a handheld printer havingoptical positioning;

FIG. 4 is a diagrammatic view in accordance with the present inventionof a more detailed version of the control arrangement of the handheldprinter having optical positioning;

FIG. 5 is a flow chart in accordance with the present invention forrepresentatively improving computational efficiency of a handheldprinter relative to signals of a position sensor;

FIG. 6 is a flow chart in accordance with the present invention forrepresentatively assessing validity of signals from a position sensor;

FIGS. 7A and 7B are graphs in accordance with the present inventionderived from signals from a position sensor that are evaluated forvalidity;

FIG. 8A is a diagrammatic view in accordance with the present inventionof a representative signal of a position sensor in matrix form;

FIG. 8B is a diagrammatic view in accordance with the present inventionof the representative signal of the position sensor in matrix form asseen in FIG. 8 with an identified target frame therein;

FIG. 9 is a diagrammatic view in accordance with the present inventionshowing the effects of a summation component acting upon arepresentative signal of a position sensor in matrix form indicative ofa previous location of the handheld printer, the summation acting upon arow;

FIG. 10 is a diagrammatic view in accordance with the present inventionshowing the effects of a representative signal of a position sensor inmatrix form indicative of a current location of the handheld printerbeing reduced in relative size;

FIGS. 11A-11D are diagrammatic views in accordance with the presentinvention showing a search for correlation between previous and currentlocations as one or more matrix frames, including searching of a reducedor smaller matrix frame of pixels indicative of the current locationbeing searched for a presence of the reduced or smaller matrix frame ofpixels indicative of the previous location;

FIG. 12 is a diagrammatic view in accordance with the present inventionshowing a correlation matrix between previous and current locations forFIGS. 10-11D;

FIG. 13 is a diagrammatic view in accordance with the present inventionshowing the effects of a summation component acting upon arepresentative signal of a position sensor in matrix form indicative ofa previous location of the handheld printer, the summation acting upon acolumn;

FIG. 14 is a diagrammatic view in accordance with the present inventionshowing the effects of a representative signal of a position sensor inmatrix form indicative of a current location of the handheld printerbeing reduced in relative size;

FIGS. 15A-15D are diagrammatic views in accordance with the presentinvention showing a search for correlation between previous and currentlocations as one or more matrix frames, including searching of a reducedor smaller matrix frame of pixels indicative of the current locationbeing searched for a presence of the reduced or smaller matrix frame ofpixels indicative of the previous location;

FIG. 16 is a diagrammatic view in accordance with the present inventionshowing a correlation matrix between previous and current locations forpreceding FIGS. 14-15D;

FIG. 17 is a diagrammatic view in accordance with the present inventionshowing the effects of anticipating movement of a target frame of pixelsbased on prior movement of the handheld printer;

FIGS. 18A-18D are diagrammatic views illustrating the computationalextensiveness which must be undertaken if an entirety of a matrix frameof pixels indicative of the previous location were searched for in anentirety of a matrix frame of pixels indicative of the current location;and

FIGS. 19-30 are diagrammatic views in accordance with the presentinvention of possible search areas to locate a presence of a matrixframe of pixels indicative of a previous location in a matrix frame ofpixels indicative of a current location.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration, specific embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention and like numerals represent like details in the variousfigures. Also, it is to be understood that other embodiments may beutilized and that process, mechanical, electrical, architectural,software and/or other changes may be made without departing from thescope of the present invention. In accordance with the presentinvention, a handheld printer for printing with optical positioning,especially by way of optical position sensors, is hereafter described.

Preliminarily, however, skilled artisans will appreciate that aniterative process occurs in evaluating signals (and attendant data) fromposition sensors in a handheld printer. That is, a current or presentsignal will over time become a previous signal, while another signalthereafter becomes another current or present signal, and so on. Inother words, that which is current becomes previous, and that which ismost recently obtained is current. The description, therefore, maysometimes refer to a current or present signal as a previous signal,when in the context of comparison to a later signal. Appreciatingembodiments of position sensors often provide an analog output thatvaries over time, this concept also extends to manipulations of theposition sensor signal itself and whether such exists in the confines ofthe sensor or in downstream processing structures and/or software,firmware, etc., such as is observed in digitized representations of ananalog output. Still further, optical position sensors often render anoutput signal that varies over time, but the information therein mayrepresent a two-dimensional array or matrix of pixels, each pixel withtheir own data. Thus, signals of position sensors, while shown hereafteras two-dimensional matrix frames of pixels of data, may also embodytheir analog counterpart, not shown, that is manipulated by the sensorand/or in downstream processing structures and/or software, firmware,etc.

For clarity, the terms pixels of data, arrays, matrix frames, matrix,matrix form, or the like, whether used singularly or as plurals, may beused interchangeably throughout the specification. Because atransformation or reduction of relative sizes of signals from positionsensors are also taught in the specification, this further translatesinto a transformation or reduction of relative sizes of matrix frames,matrices, and forms thereof, and vice versa, for the signals of positionsensors that are regularly described hereafter in matrix form. Also,representations of a matrix frame of pixels of data may have a certainmatrix size or form and, because of a later reduction in that size orform, a representation in the specification of a smaller matrix comparedto a larger matrix may be given. For example, a matrix frame may have aninitial size of 20×20 pixels of data. In reduction, it may be madesmaller into a 10×10 form, in turn, made smaller into a 1×10 or 10×1form. Alternatively, a 20×20 form may be reduced in relative size to a11×20 or 20×11 form that is searched for a presence of the 1×10 or 10×1form. This does not mean, however, that the sizes given are limiting,unless so defined in the claims, and that any matrix size is acceptableherein. The addition of extra pixels of data may also be found in areduced size of a matrix frame or signal and still be embraced by theinvention. In other words, the notion of the instant invention is notlimited by the addition of extra elements. As an example, a matrix frameof pixel data having a 20×20 matrix form that is reduced into an 11×20matrix form, further contemplates pixels above the limit of 11×20. Thatis, so long as whole or parts thereof have a reduction, the conceptapplies. From the specification below, this will become more apparent tothose of ordinary skill in the art.

With reference to FIG. 1, a handheld printer of the invention forprinting with optical positioning is given generically as 10. Itincludes a housing 14 that an operator 12 maneuvers or manipulates backand forth over a media 16 to print an image 18. In various embodiments,the image is text, figures, combinations of text and figures or thelike. They are typified in color and/or black and white and formed ofink ejected or expelled from an internal printhead. Also, the printeroptionally includes a viewable display panel 19 (dashed line) to assistthe operator during printing, such as by showing the image being printedor by providing housekeeping menus, calibration routines, or other userfeatures or options.

In FIG. 2, a representative inkjet printhead of the printer internal tothe housing [14] is shown generally as 110. It includes its own housing112 having a shape that depends upon the shape of the printer. Thehousing has at least one internal compartment 116 for holding an initialor refillable supply of ink. In one embodiment, the compartmentcontemplates a single chamber holding a supply of black, cyan, magentaor yellow ink. In other embodiments, it contemplates multiple chamberscontaining multiple different colored inks. In one instance, it includessupplies of cyan, magenta and yellow ink. In still other embodiments, itincludes plurals of black, cyan, magenta and/or yellow ink. It alsocontemplates separability from the housing 112 and/or printhead 110,despite being shown locally integrated within the housing.

At one surface 118 of the housing 112 is a portion 119 of a flexiblecircuit, especially a tape automated bond (TAB) circuit 120. At 121,another portion 121 is adhered to surface 122. Electrically, the TABcircuit 120 supports a plurality of input/output (I/O) connectors 124for connecting an actuator chip 125 (also known as a heater chip ortransducer chip) to the handheld printer during use. Pluralities ofelectrical conductors 126 exist on the TAB circuit to connect and shortthe I/O connectors 124 to the input terminals (bond pads 128) of theactuator chip 125 and skilled artisans know various techniques forfacilitating this. In an exemplary embodiment, the TAB circuit is apolyimide material and the electrical conductors and connectors arecopper or aluminum-copper. For simplicity, FIG. 2 shows eight I/Oconnectors 124, electrical conductors 126 and bond pads 128 but presentday printheads have larger quantities and any number is equally embracedherein. Also, skilled artisans will appreciate that the number ofconnectors, conductors and bond pads, while shown as equal to oneanother, may vary unequally in actual embodiments.

At 132, the actuator chip 125 contains at least one ink via that fluidlyconnects to the ink of the compartment 116. During printheadmanufacturing, the actuator chip 125 is attached to the housing with anyof a variety of adhesives, epoxies, etc., as is well known in the art.To eject ink, the actuator chip contains columns (column A-column D) offluid firing actuators, such as thermal heaters. In other actuatorchips, the fluid firing actuators embody piezoelectric elements, MEMsdevices, and the like. In either, this crowded figure simplifies theactuators as four columns of six dots or darkened circles but in actualpractice the actuators might number several dozen, hundred or thousand.Also, vertically adjacent ones of the actuators may or may not have alateral spacing gap or stagger in between. In general, the actuatorsindeed have vertical spacing, such as about 1/300^(th), 1/600^(th),1/1200^(th), or 1/2400^(th) of an inch along the longitudinal extent ofthe via. Further, the individual actuators are typically formed as aseries of thin film layers made via growth, deposition, masking,patterning, photolithography and/or etching or other processing steps ona substrate, such as silicon. A nozzle member with pluralities of nozzleholes, not shown, is adhered to or fabricated as another thin film layeron the actuator chip such that the nozzle holes generally align with andare positioned above the actuators to eject ink at times pursuant tocommands of a controller.

With reference to FIG. 3, a greatly exaggerated view of the handheldprinter 10 shows a position sensor 20 and a controller 22. The positionsensor, preferably of the optical type, includes a transmitter 24 and areceiver 26 that together shine light 28 and capture reflections 30 fromthe media 16. As is known, media surfaces have random textures (on amicro scale), which then create observable and reflected shadows uponapplication of light. Eventually, the manipulation of the signalsobtained from the sensor regarding the shadows enables understanding theposition or location of the housing, especially printhead 110, and ismade known at the controller regardless of random or predictablemovement of the housing 14 by an operator. In a basic sense, thisincludes the controller 22 being able to discern content of a signal(s)output from the position sensor, and supplied as an input to thecontroller, and correlating it to the printhead, especially itsindividual fluid firing actuators to eject ink 35 to print an image. Ina more detailed sense, this includes the controller being able tocompare a signal of the position sensor indicative of a previouslocation 23, shown as a 4×7 matrix of pixels, to a signal of theposition sensor indicative of a current location 25, shown as another4×7 matrix of pixels, each having four hatched pixels translated from afirst position 27 to a second, later position 29. Representatively, thefour hatched pixels indicate relatively dark grayscale values on themedia 16 that are observed in different orientations over time as a useror operator manipulates the housing 14 to print and image. In turn, thecontroller is to discern a difference between the previous and currentlocations and correlate same to the location of the printhead. Thecontroller need also do this quickly and efficiently, as describedbelow. In one instance, this means the controller will examine or searchthe current location for a presence, such as the four hatched pixels, ofthe previous location. To improve computational efficiency, it alsomeans the controller will reduce a relative size of the signals from theposition sensor before conducting the searching, as seen below.

In other aspects, the controller contemplates an intake checker 31between the sensor and controller, or part and parcel of the controller,to assess validity of the signal(s) of the position sensor and toarrange the information thereof such that an actual or proximaterelative distance D between the housing and the media can beascertained. It also contemplates establishment of a threshold inquirydetermining whether the housing of the printer is relatively close orfar away from the media and whether such is sufficient to conductfurther signal processing. As will be seen with reference to FIGS. 7Aand 7B, operators of the handheld printer have freedom to lift thehousing from the media and, if too far away from the media, the signalfrom the position sensor becomes fairly unusable, or invalid. On theother hand, touching the housing to the media or positioning it within apredetermined close interval renders the signal, and its attendant data,valid. Validity checking also considers application per every instanceof a signal received from the sensor or application that occursrandomly, on specified occasions or at predetermined times.

In addition, the controller 22 contemplates a to-be-printedrepresentation of an image 32, especially in bitmap form. In turn, itcorrelates the position of the printhead, especially individualactuators, to the image. It then prints the image with ink 35 on themedia 16 according to the image pattern 36 in the pixels 38. Ahas-been-printed image 34 may also be stored or accessed by thecontroller to keep track of future printing and to determine whether theimage has been printed completely or not. In structure, the controllerembodies an ASIC, discrete IC chips, FPGA's, firmware, software, amicroprocessor, combinations thereof or the like. Alternatively, theto-be-printed image 32 is dynamically updated to remove pixels that havebeen printed so that the has-been printed information 34 is merged withthe to-be-printed information. In either, the controller furtherincludes a memory to keep track of image data. The memory also includesstorage and accessibility relative to position sensor signals and theirmanipulation to compute printer location. Memory will also find utilityin general housekeeping matters, such as storage of an operating system,of sorts, display panel items, print jobs, user features, etc. In somefigures, memory will be shown, as a whole or in part, with a fairlytraditional cylinder symbol.

While not intuitive, the mentioning of a position sensor 20 as anoptical sensor structure does not mean the positioning is limited tooptics, per se. For instance, skilled artisans will appreciate that asophisticated x-y mechanical encoder could also provide position sensorinformation for reasons relating to previous and current positioninginformation. The same is also true of structures having energy in otherthan a traditionally optical range. That is, optics may include infrared(IR) or radio frequency (RF) ranges and technology. For convenience,however, all of the foregoing and any and all other hereafter developedtechnology able to provide current location information and, over time,previous location information, fall under the heading of “optical”positioning, signals, position sensors, position data, etc.

With reference to FIG. 4, a more detailed accounting of the architectureof the controller of the handheld printer is described. On a macroscale, a controller is effectively all functional components within thedashed boundary 22. Alternatively, it is only select components thereof.For instance, the intake checker 31 has already been mentioned asseparable from the controller or part of the controller. The same istrue of any of the memory cylinders shown. It is even plausible that thesensor (20) itself can be an integral part of the controller, despitebeing shown detached. Thus, skilled artisans will not prescribe anyartificial, physical or functional boundaries to the controller, unlessspecifically claimed.

In arrangement, the controller includes an intake checker 31 thatreceives the signals from the position sensor 20. Its role, then, istwofold. First, it is to assess the validity of the signal, e.g.,whether the printer housing exists close enough or too far away from themedia to be effective and such is the role of the field checkercomponent 33. Second, it is to arrange the data of the signal intocurrent and previous frames 37, 39 and such is the role of the dataarranger component 35.

With this in mind, a typical signal from the position sensor is of ananalog form that becomes converted into digital form representativelydescribed herein as frame data, matrix data, pluralities of pixelsarranged as a matrix or in matrix form, or by use of other similarlanguage. In general, this digital form consists of a two-dimensionalform of pixels having a matrix size of m×n, whereby m and n may be equalor unequal. In a representative embodiment, FIG. 8A shows a signal of aposition sensor in m×n matrix form 81, whereby both m and n equal 20(e.g. 20×20). In turn, each pixel thereof (labeled from pixel index 0 atthe m×n grid location (0, 0) to pixel index 399 at the m×n grid location(19, 19)) includes a value corresponding to a grayscale value receivedby the sensor that represents a light intensity, of sorts, of thesurface texture of the media captured at a given instance of time. Asshown later, these values typically embody one of 256 grayscale valuesthat range in value from 0 to 255, inclusive. Of course, other rangevalues for grayscale and altogether other scales are contemplated as thedata value of the matrix or any given pixel.

With reference back to FIG. 4, skilled artisans will understand that theframe data of the position sensor is a single instance of time and thatover time the values in the matrix, per each pixel, change. In thisregard, the intake checker then arranges information as a current frame37 and, over time, a previous frame 39. The process also continuallyrepeats, i.e., the current frame becomes the previous frame upon receiptof a next instance of current information in a signal from the positionsensor. The previous frame, however, is discarded to avoid issues ofoverfilling memory, so to speak. Also, the representation borne by eachof the current and the previous frame relates ultimately to a positionof the housing of the printer relative to the media. As used hereafter,the current frame is then a matrix representation of the signal of theposition sensor indicative of a current location of the printer, e.g., acurrent position frame. On the other hand, the previous frame is amatrix representation of the signal of the position sensor indicative ofa previous location of the printer, e.g., a previous position frame, andwas once a current frame earlier in time.

Within computational box 41 of the controller, a variety of functionalcomponents serve to determine a precise location of the printer, inturn, to correlate same to the printhead, especially the fluid firingactuators and to the image to-be-printed on the media. In general, thecomponents consist of: both frame and target reducers 43, 45; a targetmarket-selector 47; a target pair limiter-selector 49; a comparator 51;a highlighter 53; a navigation output calculator 55; and memories tostore and retrieve certain computations. As with the controller,however, physical boundaries are shown with each component, but are notto be limited to any artificial, physical or functional boundariesunless specifically claimed.

At a high level, the components compare the current and previous framesto find a presence of the previous frame in the current frame, in turn,ascertaining a location of the printer and printhead. To improvecomputational efficiency, the components reduce a relative size of bothframes before comparing. In this manner, the process of comparisonevaluation is sped-up and storage requirements are minimized relative tothe prior art, for example. To a lesser extent, computational efficiencycould also be realized by a reduction of a single frame, vice twoframes, and the claims support such a construction, but it is preferredto reduce both frames. Frame reduction can also occur in parallel forthe current and previous frames or in series, with either reductionoccurring first.

Remaining at a high level of discussion, FIG. 5 shows a general flow ofthis process. First, step 101 sets an initialization. That is, beforeprocessing can begin, structural or functional components of the printermay be calibrated, undergo power-up or maintenance routines, forexample. Thereafter, step 103 illustrates the reception of a signal fromthe position sensor indicative of a current location of the printer. Atstep 105, the housing is sometime thereafter manipulated by an operatorand is moved relative to the media upon which printing occurs. (At thispoint, skilled artisans should appreciate that a handheld printer is notlimited to printing on traditional media, such as paper ortransparencies. Rather, the printer can be located anywhere, because ofits mobility, and therefore print directly on a surface of an item, suchas a desk, a wall, a floor, an automobile, carpet, wood, steel, and thelist goes on indefinitely. The term media, therefore, embraces allsurfaces on which the printer can cause an image to appear. Images alsoneed not be formed with ink, as might be more prevalent in themarketplace. For example, inkjet printheads might be filled with any ofa variety of substances, such as paint, frosting, toner, or other toform pictures, cake decorations or the like.)

At steps 107 and 109, a new signal (or continuation of the previoussignal separated in time from earlier, appreciating that the positionsensor might provide its output as a contiguous analog stream of data(and/or noise) that varies over time) is received from the positionsensor, such that the signal indicative of the current location at step103 has now become a signal indicative of a previous location of theprinter and the new signal is now the signal indicative of the currentlocation of the printer. At step 111, the controller reduces therelative size of the signals, both the current and previous, to searchthe reduced signal indicative of the current location of the printer fora presence of the reduced signal indicative of the previous location ofthe printer, step 113. In that a prior signal (either embodied as aprevious or current signal) was given in matrix form as m×n, where m andn equaled one another at size 20×20, the controller will reduce the20×20 form into something less, such as 1×20, 20×1, 20×11, etc., and thesearching will examine the 20×11 form for a presence of the 1×10 form,for example, including or not intermediate reductions of size of one ormore of the matrices.

Once the comparison or searching of frames reveals the presence of theearlier in the latter, e.g., the previous in the current, the controllerwill use this information to correlate the printer to the printhead andto the image for printing. It will also keep track of this data in thesense that operators of printers often traverse the housing in a givendirection of movement, such that a history of prior movement can be usedto help minimize search areas in the current frame for a presence of theprevious frame. That is, if a movement trend is established by anoperator, the presence of the earlier data can be first examined in acertain area of the current data, to save search time. This notion,however, will be addressed in greater detail later. Returning to theflow chart, repeat processing of steps 103 through 113 occurs over andover again, for as many times necessary, to continually know position ornavigate the printer.

With reference to FIG. 6, and also at a high level of functionality, theprocess of the intake checking by way of checker 31 (FIG. 4) is that ofreceiving a signal from the position sensor, step 120. In the event thesignal is valid, step 122, the process of evaluating current andprevious frames continues at step 126. On the other hand, if the signalis invalid, its later use is avoided, step 124. Optionally, a loggingfunction may also keep track of validity versus invalidity, such thatinformation can be learned from the log. Informing certain components ofthe controller or the user of the avoiding or invalidity of the signal,step 124, may also have utility, such as by way of the viewable displayinforming the user that the position sensor needs replacing.

With reference to FIGS. 7A and 7B, more detail about the validityassessment of the position sensor is given. Reference will also be takensimultaneously to the components of FIGS. 3 and 4 (as it will forfunctionality hereafter described for other figures). The continual citeback to these other figures, however, will often be avoided to betterfacilitate the discussion of the features of the invention.

Particularly, each of FIGS. 7A and 7B show a plot 141, 143 of datapoints observed by a prototype intake checker of handheld printer,especially field checker 33, that correspond to data arranged asfrequency versus intensity. Intensity, on the one hand, corresponds tothe grayscale values of the pixels arranged in a matrix, e.g., FIG. 8A,in a range from 0-255. Frequency, on the other hand, is in contrast anappreciation of the number of actual pixels of the matrix having a givenintensity. For instance, plot 141 at position X shows about 140 pixels(of 400 pixels, e.g., a 20×20 matrix) having a grayscale value intensityof about 87, while plot 143 at position X shows about 300 pixels (of 400pixels, e.g., a 20×20 matrix) having a grayscale value intensity ofabout 75. Because of the vast difference between the number of pixelshaving grayscale values within a certain range, it can be concluded thatthe printer is either lifted too far away from the media to be a validsensor signal, e.g., plot 143, or on the surface of the media or withina predetermined close distance D to be effective, e.g., plot 141. Whatis also observed is that plot 141 shows a relatively high number ofpixels having a sufficiently high level of saturation, e.g., intensity,to be considered a valid signal, whereas the pixels of plot 143 do not.Skilled artisans will understand that the former creates a situationwhereby a position sensor near a media translates into a light sourcetransmitter near the media and brighter reflections are captured by thereceiver of the sensor. In the latter, the transmitter and receiver areso far away from the media that minimal differences exist between grayscale values of adjacent pixels prevent having a signal that is worthyof processing. To the extent the count, or frequency, reaches apre-selected threshold, the data of the sensor can be consideredinvalid. Of course, skilled artisans will be able to set their ownlevels of acceptability when determining signal validity. For example,various frequency ranges could be established whereby minimum andmaximum frequencies are observed as to whether they have too many or toofew counts or data points therein. This approach is provided for wellwhen it is appreciated that the normal distribution of the grayscalevalues of pixels creates a Gaussian-like curve when graphed. Then, whenthe sensor is too near (e.g. when the device is moved on an unevensurface) or too far (e.g. when the device is lifted) from the surface,it causes the curve to concentrate its peak in either the smaller orbigger magnitude of the distribution. Naturally, skilled artisans mayalso scrap the frequency versus intensity for some other metric ofacceptability and all such embodiments are embraced herein.

Regardless of how assessed, once the signal is deemed valid, the dataarranger 35 takes the pixels of data and converts them into current andprevious matrix frames. In the latter, a target (a subset) will beestablished that is looked for in a subset of the former. Also, thelooking-for or searching of the latter in the former, is a searching ofsorts for matching grayscale values of the pixels. Skilled artisans willappreciate that because surface imperfections in a media will yield ahigh level of light saturation for a certain portion of a media'ssurface and a low level of light saturation for another portion, if thehigh level of light saturation can be found in a first signal and thenagain in a later, second signal, a delta between the two signals can beknown. From the delta, an amount of movement can be ascertained. Forexample, consider a particularly raised surface imperfection in a mediathat yields a grayscale value of high saturation, such as a 250 value,and such is found at a grid location of (8, 8) in an m×n matrixindicative of a signal of a position sensor showing a previous frame,while all other surrounding pixels yield low grayscale saturations at avalue of 10. Over time, if an m×n matrix indicative of a signal of aposition sensor showing a current frame revealed a grayscale value of250 surrounded on all sides by grayscale values of 10, and the gridlocation of the 250 grayscale value was found at a grid location of (10,10), it can be fairly inferred that a grid movement in the pixels equals2 over and 2 down, or (10-8, 10-8). In turn, this can be directlycorrelated to the movement of the printhead and its fluid firingactuators relative to a to-be-printed image. But looking for this uniquegrayscale value in pixel data relative to a particularly raised surfaceimperfection in a media can be computationally intensive if one has toscour the entire current frame (e.g., 20×20) for the presence of theentire previous frame (e.g., 20×20). Thus, the foregoing implicates anadvantageous notion that convenience can be realized if somehow thelatter could be solely examined just for that particular grayscalenuance associated with the raised surface imperfection. Conveniencecould also be found by avoiding searching an entire current frame andjust focusing on a particular area, if somehow a past movement historyof the printer could be known.

With this in mind, and appreciating that modern position sensors willhave fairly high sample rates, a target of the previous frame to besearched for in a later or current frame is well situated by looking fora movement of a relative center in the previous frame in the currentframe. Of course, there is no requirement that the center be thelocation of the target. It is a complication, however, if a target wereestablished at an extreme boundary of a previous matrix frame and a usermanipulated the printer such that no grayscale values had commonality inthe latter frame. For at least this reason, a relative center isestablished as a target to be looked for. In functionality, it is thetarget marker-selector, component 41 (FIG. 4) that determines which is agood target to track, how big or small it should be, and what othercharacteristics it should possess. Storage and accessibility of same isalso provided for in relation to a marked target index memory 50.

With reference back to FIG. 8A, a matrix frame 81 is shown indicative ofan arrangement of pixels of data from the position sensor that will havethe same form regardless of being a current or previous frame. M×n isalso its size and m corresponds to the rows of the matrix while ncorresponds to the columns. M and n may also equal or not. Forillustration only, m and n equal hereafter. Pixel locations are alsodescribed as being of a grid location (row, column) or as an index,e.g., numbered from 0 to 399 in a row-by-row fashion in the matrix. Overtime, all signals of the position sensor will look like this figure, butwill be manipulated variously. The values per any of the pixel locationswill also change, but may be described herein with the same values, forconvenience.

With reference to FIG. 8B, a matrix frame 81-previous now corresponds toa particular signal of the position sensor that indicates a previouslocation of the printer. A center 85, a subset matrix frame, is thendeemed a “target” or target frame to-be-looked-for in a later or currentframe, not yet shown. In this example, the center has been made a 10×10matrix having pixels identified by bounding pixels 105 (found at the m×ngrid location (5, 5)), 114 (found at the m×n grid location (5, 14)), 285(found at the m×n grid location (14, 5)), and 294 (found at the m×n gridlocation (14, 14)). The center, however, can be made smaller or largeras necessary, so long as it has a size smaller than the original m×nmatrix size of the signal obtained from the sensor.

In FIG. 9, the matrix frame 81-previous is now illustrated with actualgrayscale values in each of the pixels of the m×n (e.g., 20×20) gridlocations, as opposed to simply labeling one of 400 pixel numbers from 0to 399 as in FIGS. 8A and 8B. For instance, the pixel at grid location(0, 0) is now labeled with a grayscale value of 138, whereas the pixelat grid location (19, 19) is now labeled with a grayscale value of 168.In turn, the grayscale values are obtained from the intensities observedby the position sensor from reflections from the media, during use.Also, the center 85 or target has its pixels shown with actual grayscalevalues therein. In row 5, for instance, the grayscale values of thepixels include: 167, 167, 167, 169, 173, 177, 171, 166, 165 and 164, asthe columns are traversed in order from 5 to 14. In row 14, as anotherexample, the grayscale values include 158, 165, 167, 172, 174, 183, 183,185, 183 and 181, as the columns are similarly traversed in order from 5to 14.

From here, the two-dimensions of the target are reduced into aone-dimensional form. Namely, the matrix form 87, having a single 10×1form, is the result of reducing the target. To accomplish this, avariety of techniques can be used. For instance, the target may bereduced by way of a summation component that sums either an entirety ofthe rows or the columns of the target (or a partiality of the rows orcolumns of the overall 81-previous frame). In this example, it is therows that are summed to arrive at the matrix form 87. Particularly, thesummation value at grid location (0, 1) of matrix form 87 is 1686. It isobtained by summing each of the individual grayscale values of thepixels in row 5 of the target. Thus,1686=167+167+167+169+173+177+171+166+165+164. As another example, thesummation value at grid location (9, 1) of matrix form 87 is 1751 and isobtained by summing each of the individual grayscale values of thepixels in row 14 of the target. Thus,1751=158+165+167+172+174+183+183+185+183+181. In turn, the othersummation values at grid locations (1, 1), (2, 1), (3, 1), (4, 1), (5,1), (6, 1), (7, 1) and (8, 1) are obtained by summing the grayscalevalues of each of rows 6, 7, 8, 9, 10, 11, 12 and 13 of the target,respectively. From here, it is this smaller one-dimensional matrix form87 that a presence thereof will be searched for in a later or currentframe to indicate movement of the printer. It is also where certaincomputational advantage over the prior art is achieved.

Before then, however, skilled artisans will observe that two reductionsof the matrix frame 81-previous have now occurred. That is, identifyinga target, e.g., center 85, transformed the original matrix frame ofpixels of data into a smaller or reduced target by half. Namely, theoriginal matrix frame had a two-dimensional size of 20×20, whereas thetarget only possessed a size of 10×10, e.g., the first reduction. Fromthere, the target itself was reduced into a one-dimensional form of10×1, e.g., the second reduction. The invention, however, is not limitedas to requiring both reductions or requiring one reduction in favor ofanother. Thus, a 20×20 matrix form could have been reduced to a singledimension 20×1 in the same fashion as the target was reduced, forexample. Conversely, the skipping of the second reduction into aone-dimensional form would facilitate a searching of a smaller orreduced matrix form, e.g., 10×10, in a second or current matrix formthat achieves computational advantage over scouring a 20×20 matrix formfor a previous frame in a 20×20 matrix form for a current frame. Also, areduction to a single dimension is not limited to just rows.Alternatively, it could include a reduction in form of columns such thata 1×10 matrix form results from a larger 10×10 target, as will be shownin greater detail relative to later FIGS. 13-16.

In functionality of the controller of the printer, it is the targetreducer, component 45 (FIG. 4) that accomplishes this reduction of thematrix frame 81-previous. Storage and accessibility of same is alsoprovided for in relation to a reduced target memory 52.

With reference to FIG. 10, a matrix frame 81-current now corresponds toa particular signal of the position sensor that indicates a currentlocation of the printer received later in time than the signal embodyingthe matrix frame 81-previous. The matrix frame 81-current is likewiseillustrated with actual grayscale values in each of the pixels of them×n (e.g., 20×20) grid locations, as opposed to simply labeling one of400 pixel numbers from indices 0 to 399 as in FIGS. 8A and 8B. Forinstance, the pixel at grid location (0, 0) is now labeled with agrayscale value of 136, whereas the pixel at grid location (19, 19)remains labeled with a grayscale value of 168. In turn, the grayscalevalues are obtained, as before, from the intensities observed by theposition sensor from reflections from the media, during use. To now finda presence of the previous frame in the current frame, a first preferredstep includes transforming or reducing the form of the matrix frame81-current into a reduced matrix form 91 to facilitate computation. Forthis, an m×n matrix of 20×20 form is converted into a 20×11 form. Ofcourse, other size reductions are embraced herein.

To actually arrive at the reduced matrix form 91, another plurality ofsummation functions occur. That is, a portion 93 of row 1 of matrixframe 81-current ranges in grayscale values from column 1 to column 10of 138, 143, 145, 153, 159, 164, 168, 175, 181, and 177. By addingtheses, a summation value of 1603 is obtained and is placed in the 20×11reduced matrix form 91 at grid location (1, 2) where the word SUM islocated (in later FIGS. 11A-11D, the actual 1603 summation value isshown). To arrive at the other summation values, more examples are givenso that skilled artisans will understand the process and, thus, theincremental nature of the reduction.

For instance, to get the summation value of 1563 at the one left gridlocation (1, 1) of reduced matrix form 91, the grayscale values of row 1are summed, but this time only from column 0 to column 9 of the matrixframe 81-current. Specifically, the adding of grayscale values 137, 138,143, 145, 153, 159, 164, 168, 175, and 181 corresponds to a summationvalue of 1563. Similarly, a one right grid location (1, 3) of reducedmatrix form 91 corresponds to a summation value of 1632 and is arrivedat by adding the grayscale values of row 1 of the matrix frame81-current, but only from columns 2 through 11. Specifically, the addingof grayscale values 143, 145, 153, 159, 164, 168, 175, 181, 177, and 167corresponds to a summation value of 1632. Similarly still, a two rightgrid location (1, 4) of reduced matrix form 91 corresponds to asummation value of 1651 and is arrived at by adding the grayscale valuesof row 1 of the matrix frame 81-current, but only from columns 3 through12. Specifically, the adding of grayscale values 145, 153, 159, 164,168, 175, 181, 177, 167 and 162 corresponds to a summation value of1651. This process is then similarly repeated and skilled artisans cansee the pattern to produce the summation values of the reduced matrixform 91 for all of row 1. The same is then done for each of the othernineteen rows of the twenty row matrix form, 81-current.

In functionality of the controller of the printer, it is the framereducer, component 43 (FIG. 4) that accomplishes this reduction of thematrix frame 81-current. Storage and accessibility of same is alsoprovided for in relation to a reduced frame memory 54.

With reference to FIGS. 11A-11D, the searching of the previous frame inthe current frame then consists of finding the one-dimensional reducedmatrix form 87 in the reduced matrix form 91. In that theone-dimensional reduced matrix form embodies a 10×1 form, a box 98 ofthe same dimensions or size is illustratively maneuvered through thereduced matrix form 91 until a match, or closest best option, with thereduced matrix form 87 is found. In practice, the box 98 begins at theleft hand, upper corner of the reduced matrix form 91 and progresses onecolumn to the right at a time (FIG. 11B) until the end, or upper righthand corner of the matrix is reached (FIG. 11C). It then begins again atthe left side of the matrix, but one row down or incremented from before(FIG. 11D) and progresses iteratively in this fashion to the end, e.g.,the bottom right hand corner, box 98′ in dashed line format. Of course,other traversing or maneuvering patterns are possible and skilledartisans will readily recognize them. Also, a box 98 itself is notactually formed or moved through the matrix form, but is shown toillustrate the concept of a controller performing calculations betweenthe reduced matrix form and the values within the box 98.

For actual comparison calculations between the grayscale values of theone-dimensional reduced matrix form 87 and those of the box 98 in thereduced matrix form 97, skilled artisans will observe the grayscalevalues in box 98 in FIG. 11A correspond to 1553, 1563, 1542, 1550, 1554,1567, 1583, 1601, 1587 and 1577 (in its 10×1 form), while those in box98 in FIG. 11B correspond to 1593, 1603, 1581, 1585, 1591, 1607 1613,1627, 1612 and 1598. In comparison to the grayscale values in thereduced matrix form 87 at the same grid locations of the 10×1 form, thebox 98 will either give a better comparison or match result relative toFIG. 11A or FIG. 11B.

With reference to FIG. 12, a correlation matrix 97 then results forwhich version of grayscale values in box 98 has the exact or closestbest match to the grayscale values of the reduced matrix form 87 and ahighest number means the best match. In that traversing box 98 throughthe reduced matrix form 91 in the fashion described yields 121 possiblecalculations or comparisons, the form of the correlation matrix is thenof an 11×11 form. By way of one or more distortion criteria or matchingfunctions, such as cross correlation, mean absolute difference, meansquared difference, pixel difference classification, and integralproportions, seen below, actual values are populated in the correlationmatrix. Representative equations for same include, but are not limitedto the following:

Cross  correlation$\mspace{79mu}{P_{({A,B})} = {1 - \frac{\frac{1}{N - 1}{\sum\limits_{i = 1}^{n}{( {{x_{i}}_{A} - u_{A}} )*( {x_{i_{B}} - u_{B}} )}}}{\begin{matrix}{( \sqrt{\frac{1}{N - 1}( {{\sum\limits_{i_{A} = 1}^{n}x_{i}^{2}} - {\frac{1}{N}( {\sum\limits_{i_{A} = 1}^{n}x_{i}} )^{2}}} )} )*} \\( \sqrt{\frac{1}{N - 1}( {{\sum\limits_{i_{B} = 1}^{n}x_{i}^{2}} - {\frac{1}{N}( {\sum\limits_{i_{B} = 1}^{n}x_{i}} )^{2}}} )} )\end{matrix}}}}$

Mean Absolute Difference (Mean Absolute Error)

${1/({mn})}{\sum\limits_{p = 1}^{m}{\sum\limits_{q = 1}^{n}{{{A\lbrack {p,q} \rbrack} - {B\lbrack {p,q} \rbrack}}}}}$

Mean Squared Difference (Mean Squared Error)

${1/({mn})}{\sum\limits_{p = 1}^{m}{\sum\limits_{q = 1}^{n}{{{{A\lbrack {p,q} \rbrack} - {B\lbrack {p,q} \rbrack}}}\hat{}2}}}$

Pixel Difference Classification

${1/({mn})}{\sum\limits_{p = 1}^{m}{\sum\limits_{q = 1}^{n}{{{{compare}( {{A\lbrack {p,q} \rbrack} - {B\lbrack {p,q} \rbrack}} )} \leq t}}}}$

-   -   Obtained t (threshold that determines if it is a 1 or a 0) by        getting the average difference between corresponding frame        values of both frames.

Integral  Projection$\sum\limits_{p = 1}^{m}\{ {{{\sum\limits_{q = 1}^{n}{A\lbrack {p,q} \rbrack}} - {\sum\limits_{q = 1}^{n} {B\lbrack {p,q} \rbrack} \}} + \sum\limits_{q = 1}^{n}}❘\{ {{\sum\limits_{p = 1}^{m}{A\lbrack {p,q} \rbrack}} - {\sum\limits_{p = 1}^{m} {B\lbrack {p,q} \rbrack} \}}} } $

In practice then: at grid location (0, 0) of the correlation matrix 97corresponding to the searching of FIG. 11A, for example, a correlationvalue of 0.891 is obtained; at grid location (0, 1) corresponding to thesearching of FIG. 11B, a correlation value of 0.754 is obtained; at gridlocation (0, 10) corresponding to the searching of FIG. 11C, acorrelation value of 0.919 is obtained; and at grid location (1, 0)corresponding to the searching of FIG. 11D, a correlation value of 0.778is obtained. Thus, the correlation value at grid location (0, 0) forFIG. 11A represents a better match of the grayscale values in box 98 tothe reduced matrix form 87 than does the correlation value at gridlocation (0, 1) for FIG. 11B. However, the entire correlation matrix 97is populated and the best match possible is seen as correlation value0.998 located at grid location (6, 6). As expected, it is highlyunlikely that an exact match, having a correlation value of 1.0, will befound. It is also possible that two or more grid locations may haveclose values such that one needs to be picked or selected over theother. With this in mind, skilled artisans can use knowledge of the pastto help predict the future.

That is, the original target to be searched-for in a subsequent matrix,was first selected as a relative center, e.g., grid location (5, 5) ofthe correlation matrix, and has now moved to grid location (6, 6). Thus,a movement of 1 column over and 1 row down has been observed and mayprovide a clue for the future movement of the printer. If the patternholds true, the next search between current and previous frames wouldreveal a best match at grid location (7, 7) of the correlation matrix,and then at (8, 8) and so on. Based on this, knowledge of the past canthen be used to discriminate ties between two or more correlation valuesand also help establish a possible search area, described further belowin detail, to save computational time by avoiding looking at the entirecurrent frame for a presence of the previous frame.

In functionality of the controller of the printer, it is the target pairlimiter-selector, component 49 (FIG. 4) that accomplishes this “where tolook” functionality for finding the one-dimensional reduced matrix form87 in the reduced matrix form 91. Also, it is the comparator, component51 (FIG. 4) that accomplishes the actual searching and finding, or not,of the previous frame in the current frame, such as by examination ofthe correlation matrix. Storage and accessibility of same is alsoprovided for in relation to a comparison results memory 56.

With reference to FIGS. 13, 14, 15A-15D and 16, a process of finding apresence of a previous frame in a current frame to ascertain printermovement is similar to that of 9, 10, 11A-11D and 12, respectively. Theprimary difference, however, lies in the notion that the former figuresarrange the previous frame as a reduced version in a one-dimensionalform in a single row form, vice column, while the current frame isreduced, such as from a 20×20 form to an 11×20 form, by summinggrayscale values in columns, vice rows. Searching the reduced currentframe for a presence of the reduced previous frame then proceeds by wayof rows, vice columns. In all other regards, the process is the same. Italso provides representative examples of how skilled artisans will beable to further take advantage of the notions of the invention withoutneeding to describe the nearly endless varieties of computations.

With reference to FIG. 13, a matrix frame 181-previous corresponds to aparticular signal of the position sensor that indicates a previouslocation of the printer and a center 185, a subset matrix frame, isfound in the same fashion as the center 85 of FIG. 8B. The center isthen deemed a to-be-looked-for “target” in a later or current frame, notyet shown. In the example, the center has been made a 10×10 matrixhaving pixels identified by bounding pixels, from FIG. 8B, numbered 105(found at the m×n grid location (5, 5)), 114 (found at the m×n gridlocation (5, 14)), 285 (found at the m×n grid location (14, 5)), and 294(found at the m×n grid location (14, 14)). In FIG. 13, the boundingpixels, as well as all pixels, are now illustrated with actual grayscalevalues in each of the pixels of the m×n (e.g., 20×20) grid locations, asopposed to simply labeling one of 400 pixel numbers from indices 0 to399 as in FIGS. 8A and 8B. For instance, the pixel at grid location (0,0) is now labeled with a grayscale value of 138, whereas the pixel atgrid location (19, 19) remains labeled with a grayscale value of 168. Inturn, the grayscale values are obtained from the intensities observed bythe position sensor from reflections from the media, during use. Also,the center 185 or target has its pixels shown with actual grayscalevalues therein. In row 5, for instance, the grayscale values of thepixels include: 167, 167, 167, 169, 173, 177, 171, 166, 165 and 164, asthe columns are traversed in order from 5 to 14. In row 14, as anotherexample, the grayscale values include 158, 165, 167, 172, 174, 183, 183,185, 183 and 181, as the columns are traversed in order from 5 to 14.

From here, the two-dimensions of the target are reduced into aone-dimensional form. Namely, the matrix form 187 having a single 1×10form. To accomplish this, a variety of techniques can be used. In arepresentative embodiment, it is accomplished by a summation componentfor either an entirety of the rows or the columns of the target. In thisexample, it is the columns that are summed to arrive at the matrix form187. Particularly, the summation value at grid location (1, 0) of matrixform 187 is 1639. It is obtained by summing each of the individualgrayscale values of the pixels in column 5 of the target. Thus,1639=167+168+166+164+165+165+165+161+160+158. As another example, thesummation value at grid location (1, 9) of matrix form 187 is 1716. Itis obtained by summing each of the individual grayscale values of thepixels in column 14 of the target. Thus,1716=164+162+165+168+170+174+174+179+179+181. The other summation valuesat grid locations (1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6), (1, 7)and (1, 8) are obtained by summing the grayscale values of each ofcolumns 6, 7, 8, 9, 10, 11, 12 and 13 of the target, respectively. Fromhere, it is this smaller one-dimensional matrix form 187 that a presencewill be searched for in a later or current frame to indicate movement ofthe printer. It is also where certain computational advantage over theprior art is achieved.

Before then, however, skilled artisans will also observe that anothertwo reductions of the matrix frame 181-previous have now occurred. Thatis, identifying a target, e.g., center 185, transformed the originalmatrix frame of pixels of data into a smaller or reduced target by half.Namely, the original matrix frame had a two-dimensional size of 20×20,whereas the target only possessed a size of 10×10, e.g., the firstreduction. From there, the target itself was reduced into aone-dimensional form of 1×10, e.g., the second reduction. The invention,however, is not limited as to requiring both reductions or requiring onereduction in favor of another. Thus, a 20×20 matrix form could have beenreduced to a single dimension 1×20 in the same fashion as the target wasreduced, for example. Conversely, the skipping of the second reductioninto a one-dimensional form would facilitate a searching of a smaller orreduced matrix form, e.g., 10×10, in a second or current matrix formthat achieves computational advantage over scouring a 20×20 matrix formfor a previous frame in a 20×20 matrix form for a current frame.

In functionality, it is again the target reducer, component 45 (FIG. 4)that accomplishes this reduction of the matrix frame 181-previous.Storage and accessibility of same is also provided for in relation to areduced target memory 52.

With reference to FIG. 14, a matrix frame 181-current now corresponds toa particular signal of the position sensor that indicates a currentlocation of the printer received later in time than the signal embodyingthe matrix frame 181-previous. The matrix frame 181-current is likewiseillustrated with actual grayscale values in each of the pixels of them×n (e.g., 20×20) grid locations, as opposed to simply labeling one of400 pixel numbers from indices 0 to 399 as in FIGS. 8A and 8B. Forinstance, the pixel at grid location (0, 0) is now labeled with agrayscale value of 136, whereas the pixel at grid location (19, 19)remains labeled with a grayscale value of 168. In turn, the grayscalevalues are obtained from the intensities observed by the position sensorfrom reflections from the media, during use. To now find a presence ofthe previous frame in the current frame, a first preferred step includestransforming or reducing the form of the matrix frame 181-current into areduced matrix form 191 to facilitate computation. For this, an m×nmatrix is converted of 20×20 form is converted into an 11×20 form. Ofcourse, other sizes reductions are embraced herein.

To actually arrive at the reduced matrix form 191, another plurality ofsummation functions occur. For example, a portion 193 of column 1ranging from row 1 to row 10 includes grayscale values of 138, 137, 141,142, 140, 145, 148, 148, 146, and 147. By adding theses, a summationvalue of 1432 is obtained and is placed in the 11×20 reduced matrix form191 at grid location (1, 1) where the word SUM is located (in laterFIGS. 15A-15D, the actual 1432 value is shown). To arrive at the othersummation values, the same process as FIG. 10 occurs, but only forcolumns until an entirety of the twenty-column matrix is filled.

In functionality, it is again the frame reducer, component 43 (FIG. 4)that accomplishes this reduction of the matrix frame 181-current.Storage and accessibility of same is also provided for in relation to areduced frame memory 54.

With reference to FIGS. 15A-15D, the searching of the previous frame inthe current frame consists of finding the one-dimensional reduced matrixform 187 in the reduced matrix form 191. In that the reduced matrix formembodies a 1×10 form, a box 198 of the same size is illustrativelymaneuvered through the reduced matrix form until a match, or closestbest option, with the reduced matrix form 187 is found. In practice, thebox 198 begins at the left hand, upper corner of the reduced matrix formand progresses one column to the right at a time (FIG. 15B) until theend, or upper right hand corner of the matrix is reached (FIG. 15C). Itthen begins again at the left side of the matrix, but one row down orincremented from before (FIG. 15D) and progresses iteratively in thisfashion to the end, e.g., the bottom right hand corner, box 198′ indashed line format. Of course, other traversing or maneuvering patternsare possible and skilled artisans will readily recognize them. Also, abox 198 itself is not actually formed or moved through the matrix form,but is shown to illustrate the concept of a controller performingcalculations between the reduced matrix form and the values within thebox 198.

For comparison calculations, skilled artisans will observe the grayscalevalues in box 198 in FIG. 15A correspond to 1412, 1422, 1455, 1501,1564, 1602, 1628, 1667, 1686 and 1740 in its 1×10 form, while those inbox 198 in FIG. 15B correspond to 1422, 1455, 1501, 1564, 1602, 1628,1667, 1686, 1740 and 1745. In comparison to the grayscale values in thereduced matrix form 187 at the same grid locations of the 1×10 form, thebox 198 will either give a better comparison or match result relative toFIG. 15A or FIG. 15B (this same is true of the other figures too, butonly these two are used for comparison).

With reference to FIG. 16, a correlation matrix 197 is the ultimateresult of which version of grayscale values in box 198 has the exact orclosest best match to the grayscale values of the reduced matrix form187. In that traversing the box 198 through the reduced matrix form 191,in the fashion described, yields 121 possible calculations orcomparisons, the form of the correlation matrix is an 11×11 form. By wayof one or more distortion criteria or matching functions, previouslyshown, values are populated in the correlation matrix. Namely, at gridlocation (0, 0) corresponding to the searching of FIG. 15A, acorrelation value of 0.8 is obtained. At grid location (0, 1)corresponding to the searching of FIG. 15B, a correlation value of 0.838is obtained. At grid location (0, 10) corresponding to the searching ofFIG. 11C, a correlation value of −0.884 is obtained. At grid location(1, 0) corresponding to the searching of FIG. 15D, a correlation valueof 0.806 is obtained. Thus, the correlation value at grid location(0, 1) for FIG. 15B represents a better match (e.g., higher score) ofthe grayscale values in box 198 to the reduced matrix form 187 than doesthe correlation value at grid location (0, 0) for FIG. 15A. However, theentire correlation matrix 197 is populated and the best possible matchis seen as correlation value 0.998 located at grid location (6, 6). Asbefore, it is highly unlikely that an exact match, having a correlationvalue of 1.0, will be found. It is also possible that two or more gridlocations may have close values such that one needs to be picked orselected over the other. With this in mind, skilled artisans can useknowledge of the past to help predict the future as seen earlier.

With reference to FIG. 17, skilled artisans will appreciate that theremay be times when tracking a printer movement history becomesproblematic. For example, consider a target 150 (5×5 form) beingsearched for in a matrix frame 152 (20×20 form). To the extent a userhas a history of moving the printer three columns to the right and tworows down (arrow A), a moved target would then be found at 150′ (alsoknown as “target pairs,” e.g., target 150 from the previous and target150 from the current). If the starting target were not reference numeral150 in the upper left hand corner of the matrix frame 152, but referencenumeral 154 in the upper right hand corner of the matrix frame 152, amovement of three columns to the right and two rows down (arrow B) wouldyield a partial null set 156. Thus, contemplation of another target ortarget pairs is in order. Also, redefining a boundary in which targetpairs is calculated is possible. For this, simply tracking the target150 (or its reduced one-dimensional counterpart) in the matrix frame152, according to known past history, implicates the stopping ofsearching the matrix frame when considering past movement. Thus, thelast possible position of the pair (e.g., the previous target 150 andthen the current target 150′) along row 0 is when the index of thetarget's pair reaches column 12, which is three (column movement) lessthe number of columns in the default boundary (dashed line 160) area.For succeeding rows, the index of the target's pair is only until therow 13, which is 2 (row movement) less the number of rows in the defaultboundary (“db” arrow area). This new boundary condition (“new” arrowarea) is determined by the target pair limiter-selector 49 (FIG. 4) sothat the comparator 51 will know which set of values are to be comparedwith the target.

In other words, the target pair limiter-selector 49 decides what part ofthe current frame will be used for comparison with the marked target.All possible target-sized values in the current frame are determined,traversed and compared with the target within the comparator 51 throughthe previously mentioned distortion criterion or matching functions suchas cross correlation, mean absolute difference, mean square difference,pixel difference classification, integral proportions, or a combinationof such methods. From there, the result of comparing the reduced target(previous) and one of the possible target-sized values in the reduced(current) frame will be stored in the comparison results memory 56. Overtime, this process is repeated up to the number of all the possibletarget-sized values within the boundary set by the target pairlimiter-selector 49. When that number is reached, the highlighter 53will determine the minimum value in the comparison results memory 56.

With reference to FIGS. 18A-18D, advantage of the invention by reducingthe relative size of the current and previous frames for searchingpurposes will be illustrated. Namely, consider that the targetmarker-selector 47 (FIG. 4) chooses the center 85 (FIGS. 8B and 9) ofthe previous frame as the default target 180 (e.g. a 10×10 form). In thenormal comparison with the current frame 190 (e.g., a 20×20 form), allpossible target-sized values (e.g., 10×10 forms) in the current frameare searched. By beginning at the upper left hand indexes of the data inthe current frame 190 (FIG. 18A), traversal occurs by one columnincrements at a time (FIG. 18B) until an end of the row is reached (FIG.18C). From there, FIG. 18D shows the increment of one row and traversalcontinues in this manner for the target 180 in the current frame 190until all rows and columns are contemplated, such as when the target isshown as 180′ (dashed box). If you consider a matrix form of N×N(rows×columns), there will be (N+1)² indexes to be traversed. This,however, is more computationally extensive than by reducing a relativesize of both the target and the current frame, especially consideringthe navigation of the instant invention prefers to only search and makecomputations in those portions of the current frame where the target ismost likely found, e.g., possible search area, based on predictingfuture movement of the printer based on the past history of movement.

With reference to FIGS. 19-30, a representative process for defining thepossible search area is described. As previously mentioned, thesearching of the previous frame for a presence in the current frameoccurs by looping or traversing the previous frame through an entiretyof the current frame, and such also occurs, preferably, with a reducedversion of a relative size of both the previous and current frames. FIG.19, however, is used to simply illustrate that looping the targetthrough the current frame results in 121 comparison results overall andfinishes at index 210 (overlap of the gray portions of the matrix frame155). For FIG. 20, consider the current frame as reference element 218having a 20×20 matrix form. The previous frame, on the other hand, isselected as reference element 220 and exists in the center of thecurrent frame. It has a 10×10 form and is bounded by pixels at indices105, 114, 285 and 294. For past movement, assume a course of up one rowand left one column occurred such that the target is expected at element222 having bounding pixels at indices 84, 93, 264 and 273. However,searching solely at element 222 does not guarantee the finding of theactual location of the target because it does not take intoconsideration potential abrupt changes in a user's maneuvering of theprinter. To the extent computations are conducted simply based onborders of targets, this then limits the searching to four indices,e.g., 2×2 indices occurring at 85, 85, 104, and 105 by which to find thetarget. Again, no guarantees of finding the target are given for lack ofconsidering abrupt user maneuvering.

To remedy this, there is a possible search area (PSA) tolerance valuethat increases the PSA in which the target can be found. Naturally, thetolerance value could be large or small depending upon computationalpreference. Sampling frequencies, basic assumptions and other criteriawould be typical information used in setting or selecting its precisevalue. As a representative example, consider a PSA tolerance value=1,whereby the possible search area is increased by one row and column inall directions, such that adding 1 column to the left, 1 column to theright, 1 row on top, and 1 row at the bottom increases the PSA to 4×4,element 225. For this, there is then sixteen correlation coefficients(e.g., from the correlation matrix) to be searched, as opposed to 121coefficients. On the other hand, if the PSA tolerance value were toequal two, there would then be thirty six correlation coefficients asseen by element 227.

In FIG. 21, the PSA tolerance value is shown as three as evidenced byelement 229. In turn, the computation of the target's movement can beobtained faster by about a half rate when compared to an entire framesearch, and still is found to consider the abrupt movement of the targetup to a magnitude of (4, ±4) based from the expected movement of (−1,−1) (e.g., one row and column movement in the up and left directions, asopposed to a (+) stylized movement in the down and right direction) plusthe tolerance (±3, ±3).

In the remaining FIGS. 23-30, still other situations are shown where thePSA tolerance value equals three, but with other caveats. In general,however, the PSA is shown as a bounding rectangle, element 250, andincludes labeled indices or pixel locations avoiding X's therein. Also,that which corresponds to the bounding rectangle 220 shows the previouslocation of the target in the previous frame. The thick borderline 275inside the frame 218 is the expected location of the target in theseframes (i.e. the current frame). Of course, skilled artisans will beable to comprehend other scenarios and all are embraced herein.

As a result, the below table summarizes certain improvements of theinvention:

-   -   Wherein, Target size: 10×10    -   Frame size: 20×20    -   Target movement: for example, −1 (column), −1 (row) per frame,        where target selected is the center of the Previous Frame 5.

TABLE PSA Tolerance No. of comparison Target search method Value resultsEntire frame (correlation matrix) 0  121 (11 × 11) search Based onprevious movement 0  4 (2 × 2) only Based on previous movement 1 16 (4 ×4) plus PSA tolerance value Based on previous movement 2 36 (6 × 6) plusPSA tolerance value Based on previous movement 3 64 (8 × 8) plus PSAtolerance value

Aside from the aforementioned method of determining the PSA where thetolerance value is determined based on the maximum possible movement ofthe target, there are several other approaches on minimizing the area tosearch for the target. For example, the PSA before was increased in alldirections (all sides) regardless the direction of the target's movementof one row up and one column left. In other embodiments, it is expectedto only increase the PSA on sides thereof anticipating target movement.It also contemplates an addition of at least 1 row or column in anopposite side of movement based on a change of direction of the printer,since after the deceleration just before switching the direction ofmotion, it will come to a state where the target has stopped moving inpreparation for a movement to the other direction. The minimum additionto the opposite direction is a method used just in case the samplingrate could not catch up and the no-movement state was not captured. Thiscan be increased up to a value less than the set PA tolerance. Withreference to FIG. 22, this is seen by providing a tolerance value of thePSA asymmetrically. In this example, to anticipate the changes indirection of the target's movement, the element 231 has two less rowsand columns, such as at elements 233 and 235, in comparison to element229 in FIG. 21.

Another way to accomplish this is by setting a threshold for the valueof the peak comparison result before increasing the PSA of the target'snext location. For example, using correlation, e.g., correlation matrix(FIG. 12 or 16), if a given threshold is set at a correlation value of0.98 and a maximum possible correlation result between a reducedprevious frame within a reduced current frame is found to be less thanthe threshold, such as at 0.95, it can be assumed that the real targetcould still be outside the possible search area computed. Thus, the PSAcould be made ever expanding, such as by adding rows and/or columns andcomputing correlation values for the additions only.

Other expanding of the PSA can be accomplished as follows. For instance,a minimum PSA tolerance value could be set, such as to one. In theevent, a best match is not found between a previous and current frame,an increase of the tolerance value could then occur to two, for example,and so on. Stopping the increase could then occur when the maximumcorrelation value, e.g., the correlation matrix (of the increasedtolerance values) is less than the existing or previous maximumcorrelation value.

In any embodiment, certain advantages of the invention over the priorart are readily apparent. For example, the invention at hand providesenhanced computation processing for navigating a handheld printer,ultimately improving print quality regardless of user manipulation. Italso adds a simple architecture for performing same. Position signalvalidity checking and PSA, including tolerance values, or not, are othernoteworthy features.

Finally, one of ordinary skill in the art will recognize that additionalembodiments are also possible without departing from the teachings ofthe present invention. This detailed description, and particularly thespecific details of the exemplary embodiments disclosed herein, is givenprimarily for clarity of understanding, and no unnecessary limitationsare to be imported, for modifications will become obvious to thoseskilled in the art upon reading this disclosure and may be made withoutdeparting from the spirit or scope of the invention. Relatively apparentmodifications, of course, include combining the various features of oneor more figures with the features of one or more of other figures.

1. A handheld printer to be manipulated back and forth by an operatorover a media during use to print an image on the media, comprising: ahand maneuverable housing for the operator; an inkjet printhead on or inthe housing to print the image; a controller communicating with theprinthead to cause printing or not; a position sensor for directinglight at the media and communicating with the controller to provide alocation of the printhead during use, an output of the position sensorproviding information indicating a current location of the housing andover time a previous location of the housing; a reducer for altering arelative size of the output of the position sensor into a reducedcurrent location and a reduced previous location, wherein the reducertwice alters the relative size of the previous location to obtain thereduced previous location but only once alters the relative size of thecurrent location to obtain the reduced current version; and a comparatorto compare the reduced current location to the reduced previous locationand find the reduced previous location in the reduced current location,wherein the controller ascertains a relative location of the printheadto the image upon finding the reduced previous location in the reducedcurrent location.
 2. The handheld printer of claim 1, wherein thereducer or comparator are part of the controller.
 3. The handheldprinter of claim 1, wherein the reducer further includes a targetreducer and a frame reducer.
 4. The handheld printer of claim 1, whereinthe output of the position sensor provides a plurality of pixels in amatrix frame of two-dimensional form corresponding to gray scale valuesimaged by the position sensor, wherein the twice altering of therelative size of the previous location includes a first altering thateliminates edge data pixels from the matrix frame by selectingcentermost data pixels from the matrix frame and a second altering thatreduces the centermost data pixels from the two-dimensional form into aone dimensional form, and wherein the once altering of the relative sizeof the current location includes maintaining the reduced previouslocation as another two-dimensional form.
 5. The handheld printer ofclaim 1, wherein the output of the position sensor provides a pluralityof pixels in a matrix frame of rows and column, further including asummation component for summing pixel values of either a full or partialrow or column of the matrix frame to accomplish the altering therelative size of the output of the position sensor.
 6. The handheldprinter of claim 1, further including an intake checker as part of thecontroller or not to ascertain whether the output of the position sensorrepresents a valid or invalid signal corresponding to the housing beingrelatively close or far from the media, respectively.
 7. The handheldprinter of claim 1, further including a limiter that focuses thecomparator for comparing and finding the reduced previous location inthe reduced current location.
 8. The handheld printer of claim 1,further including a selector for determining which portion of the outputof the position sensor will be altered in relative size by the reducer.9. The handheld printer of claim 1, further including a navigationoutput calculator that utilizes and keeps track of a previous movementhistory of the housing.
 10. A handheld printer to be manipulated backand forth by an operator over a media during use to print an image onthe media, comprising: a hand maneuverable housing for the operator; aninkjet printhead on or in the housing to print the image; a controllercommunicating with the printhead to cause printing or not; a positionsensor communicating with the controller to provide an output of valuesindicative of a current location and over time a previous location ofthe printhead, wherein the controller correlates the location of theprinthead to the image, the controller further including, a reducer foraltering a relative size of the output of values of the position sensorinto a reduced current location and a reduced previous location, whereinthe reducer twice alters the relative size of the previous location suchthat a first altering eliminates data pixels from an edge of the outputof values of the position sensor and a second altering reduces remainingpixels of the output values of the position sensor into a combinedrepresentation of the remaining pixels and the reducer only once altersthe relative size of the current location; and a comparator to comparethe reduced current location to the reduced previous location and findthe reduced previous location in the reduced current location, whereinthe controller ascertains a relative location of the printhead to theimage upon finding the reduced previous location in the reduced currentlocation according to examination of a correlation between the output ofvalues.
 11. The handheld printer of claim 10, wherein the controllercreates a correlation matrix for the output of values that is tracked toascertain movement history of the housing.
 12. The handheld printer ofclaim 10, wherein the reducer further includes a reducer component foreach of the output of values indicative of the current location and theprevious location.
 13. The handheld printer of claim 10, wherein thecontroller further includes a selector for determining which portion ofthe output of values of the position sensor will be altered in relativesize by the reducer.
 14. The handheld printer of claim 10, wherein thecontroller further includes a selector to determine a possible searcharea for finding the reduced previous location in the reduced currentlocation according to examination of the correlation between the outputof values.
 15. In a handheld printer having a housing to be manipulatedback and forth by an operator over a media during use to print an imageon the media, a method of navigating the housing, comprising: providinga position sensor on or in the housing; receiving an output signal ofthe position sensor indicative of a location of the housing;ascertaining whether the output signal of the position sensor representsthe housing being relatively close or far from the media; after theascertaining, sorting the output signal into a plurality of valuesindicative of both a current and previous location of the housing; afterthe sorting, reducing a relative size of the plurality of values foreither the current or previous location of the housing, or both; andafter the reducing, examining the plurality of values for the currentlocation of the housing for a presence of the plurality of values forthe previous location of the housing.
 16. The method of claim 15,wherein the reducing the relative size includes arranging the pluralityof values into a matrix form having rows and columns, further includingsumming either a full or partial row or column of the matrix form. 17.The method of claim 15, tracking a prior movement history of thehousing.
 18. The method of claim 17, further including using the priormovement history of the housing for the step of the examining theplurality of values for the current location of the housing for thepresence of the plurality of values for the previous location of thehousing.